Welcome to this thread! Here, I would like to explain that using and modifying MCPE's NBT (including Compound, List, etc) Tags is completely possible.
MCPE has always used the NBT saving system to save and store data inside our world files. But now that 0.12 is out, with all the Enchanting and Renaming features that got added, the possibilities are now infinite.
What do we rely on to take advantage of these?
In addons mainly, and external inventory editors.
What can and can't be modified?
MCPE has many editable NBT Tags, but not the same as PC. For example, MCPC has a NBT Tag for Creeper entities that can modify the size of its explosion; it's called "Fuse". In the other side, MCPE lacks of this one. But, if we speak of the "SkeletonType" Skeleton NBT Tag, both platforms have it and can be modified. Sadly, MCPE bugs on this one.
I am currently working on a list of the NBT Tags each entity has, and is very extense